This invention is in the field of sewing machines; more specifically, an electronically controlled sewing machine having the capability of producing a buttonhole in two steps where the length of the buttonhole is visually controlled by an operator.
It is known in the prior art to have a sewing machine complete a buttonhole in four steps, one step for each of the bars and the legs of the buttonhole. It is also known in the prior art to make a sewing machine, at somewhat increased manufacturing cost, capable of producing a buttonhole in two steps consisting each of a barring stitch and a leg. The prior art also teaches sewing machines having the capability to produce a buttonhole in one step without further operator intervention once initiated, however at still further manufacturing cost and generally requiring a special purpose buttonholing presser foot and careful initial operator preparation. The use of a sewing machine having the capability for one step buttonholing offers many advantages particularly when a garment being operated upon requires the stitching of many identical buttonholes. However, the greatly increased manufacturing costs of such a one step buttonholing machine and the requirement for a relatively expensive special purpose buttonholing foot will, in many cases, outweigh the convenience thereby attained. For many sewing machine operators, a sewing machine having the capability of performing a buttonhole in two steps is an attractive compromise between the much more expensive sewing machine having a one step buttonholing capability, and the slightly less expensive, but more tedious operations required of a sewing machine having the capability to perform a buttonhole in four steps.
In the prior art sewing machines having the capability to perform buttonholes in two steps, provision must be made for operator initiation of the second step of the buttonhole. In many of the prior art machines, such as is shown in U.S. Pat. No. 3,754,521 of Thuring, a special control is provided operative only for initiating the second step of the buttonhole. In the U.S. Pat. No. 3,060,875 of Iida, actuation of the second step of the buttonhole is implemented by depression of the reverse button which has previously been rotated 90.degree. in order to present a cam surface part of the reverse button to a lever arrangement of the bight controlling mechanism so that opposite side stitches of a buttonhole will be initiated. However, the construction disclosed in the last cited patent is effective only to accomplish a four step buttonhole and, further, is susceptible of erroneous operation in normal sewing and buttonhole stitching because of the required 90.degree. rotation of the reverse button in order to accomplish buttonhole stitching.
In an electronically controlled sewing machine, such as is shown in U.S. Pat. No. 3,977,338 of Wurst et al, one step buttonholing is accommodated by the use of a presser device, as shown in the U.S. Pat. No. 3,877,403 of Ketterer, used in conjunction with a lever device, as shown in the U.S. Pat. No. 3,841,246 of Casner et al, modified, however, to accommodate a switch device for automatically signaling the electronics of the sewing machine at the termination of the first step of the buttonhole. In order to accommodate the two step buttonhole in the prior art electronically controlled sewing machines it has been necessary for an operator to manually manipulate the tripping rod lever shown in the U.S. Pat. No. 3,841,246 in order to initiate the second step of a two step buttonhole. Unfortunately, the two step buttonholing thus accommodated in an electronically controlled sewing machine was somewhat inconvenient to the use of an operator, was somewhat hazardous and, still required the addition to the sewing machine of some of those parts necessary to accommodate one step buttonholing.
What is required is an electronically controlled sewing machine of economic construction for two step buttonholing capability which is not susceptible of erroneous operation and will not increase the hazard to the operator or to damage of work material.